Angle of reflection = angle of incidence (B) Use Snell's law. n1/n2 = sin(theta1)/sin(theta2) But in order to use snell's law, you need to get the ratio of n's first. You can do that, though, using the fact that light incoming at the critical angle refracts at 90 degrees. n1/n2 = sin(critical angle)/sin(90 degrees)= sin (critical angle) Therefore, for your answer to part (B) sin (refracted angle) = sin (incident angle)sin(critical angle).